The present invention relates generally to electrical circuits and, more particularly, to a system and method to boost an input bias to facilitate driving a load.
A hard disk drive system generally includes one or more rotating disks or platters on which data is stored as a sequence of magnetically polarized regions on the surface of the disk. An associated read/write head is associated with each surface of the disk on which data can be stored. The read/write head includes a small coil (or winding) of wire through which current flows to read or write data relative to the disks.
For example, a write head employs an inductive coil, which is selectively energized to generate magnetic fields that form magnetic patterns on the surface of the disk representing binary data (e.g., ones and zeros). The orientation of the patterns depends on the direction of electrical current flow through the inductive coil. That is, writing binary data entails selectively changing, or reversing, the direction of current flow through the head.
The direction of current flow through the coil is the controlled by a preamplifier, often referred to as a write driver. In order to write data, the write driver drives electric current through the inductive write head to create a temporary magnetic field that magnetizes a small region of the disk at the present position of the write head.
The write driver reverses current through the head based on a command signal from associated controls, which represents the data to be stored. The speed at which data can be stored is determined, at least in part, according to how fast the current through the write head can be reversed in response to the bit pattern of the command signal. It is desirable to facilitate the reversal of current through the head, so as to increase the speed at which data can be stored on the magnetic storage medium. The faster data can be stored on the rotating disk also enables an increase in the data density, as magnetically polarized regions on the disk surface can be packed more closely together.
Various approaches have been employed in efforts to improve the speed of reversing write current through an inductive head. Such approaches, however, have not been completely satisfactory; often providing either complex or inflexible solutions.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention relates generally to boosting biasing of a load so as to facilitate reversing the direction (e.g., a polarity change) of the biasing relative to the load. For example, the system can control boost current (e.g., overshoot or undershoot) applied to the load so as to improve the rise or fall time associated with reversing the load current. The amount of boosting can be programmable, for example, by setting an adjustable boost voltage that is used to bias the boost current applied for a duration associated with each reversal of current through the load. The duration of the boosting also can be programmable. The present approach thus is flexible, as it can be adapted to help improve performance of various driver systems (e.g., write drivers), including those implemented with various different configurations of write heads or control circuitry.
Another aspect of the present invention relates generally to a methodology to facilitate reversing a direction of write current through a write head. Such methodology applies desired boosting based on a programmable boost voltage in response to reversing direction of the write current through a write head. The direction of the boosting depends on the direction change of the write current relative to the write head.